WinUI 3 Selected Items from ListView send with CommandParameter

Question

I have a WinUI 3 project scaffolded with Template Studio. A ListView with Multiple selection mode. I use MVVM, so binding through commands to the view model. When I change selections inside my list, the program enters my method which is good. But my parameter is null.

How can I when I change selections inside my list to send the elements to a method inside my view model. CommandParameter="{Binding}" might be the problem.

MyPage.xaml

<ListView
    SelectionMode="Multiple"
    ItemsSource="{x:Bind ViewModel.ValidationFlagsList, Mode=OneTime}"
    SelectedValuePath="Key"
    DisplayMemberPath="Value">
    <interactivity:Interaction.Behaviors>
        <core:EventTriggerBehavior EventName="SelectionChanged">
            <core:InvokeCommandAction Command="{x:Bind ViewModel.FlagCheckBoxChangedCommand}" CommandParameter="{Binding}" /> 
        </core:EventTriggerBehavior>
    </interactivity:Interaction.Behaviors>
</ListView>

MyViewModel.cs

public IEnumerable<KeyValuePair<string, string>> ValidationFlagsList => EnumExtensions.GetAllValuesAndDescriptions<ValidationFlag>();

public ICommand FlagCheckBoxChangedCommand { get; }

ctor() 
{
    FlagCheckBoxChangedCommand = new RelayCommand<object>(FlagCheckBox_Changed);
}


private void FlagCheckBox_Changed(object validationFlag)
{
    // Problem: method is called, but parameter is null
}

Andrew KeepCoding · Accepted Answer · 2023-05-02 08:29:39Z

1

You just need to remove the CommandParameter and the SelectionChangedEventArgs will be passed to the command.

<ListView
    DisplayMemberPath="Value"
    ItemsSource="{x:Bind ViewModel.ValidationFlagsList, Mode=OneTime}"
    SelectedValuePath="Key"
    SelectionMode="Multiple">
    <interactivity:Interaction.Behaviors>
        <core:EventTriggerBehavior EventName="SelectionChanged">
            <core:InvokeCommandAction Command="{x:Bind ViewModel.FlagCheckBoxChangedCommand}" />
        </core:EventTriggerBehavior>
    </interactivity:Interaction.Behaviors>
</ListView>

Then in SelectionChangedEventArgs, you'll get AddedItems and RemovedItems.

BTW, the ListView has a SelectedItems property but it's just a plain property and not a DependencyProperty, so unfortunately you can't use it in bindings. Here's a workaround if you are interested.

edited May 2, 2023 at 8:29

answered May 2, 2023 at 8:21

Andrew KeepCoding

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2 Comments

Mihai Socaciu Over a year ago

It works now. But should I import this module in a ViewModel using Microsoft.UI.Xaml.Controls;? It's required for parameter SelectionChangedEventArgs. Is it relevant more to Code-Behind approach?

Andrew KeepCoding Over a year ago

I don't think so. That is just namespace, not a module.

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